Reducing power consumption is one of the most important challenges when designing the wireless transmit/receive units (WTRUs). Increased bandwidth, higher data rates and multimedia user interfaces result in higher power demands for new WTRUs as compared to previous generations of WTRUs.
The DRX mode is intended to identify periods of relative inactivity of the WTRU, which provides opportunities to conserve battery power by powering down various on-board components in the WTRU. The WTRU is informed of occasions when the WTRU must wake up to receive transport information.
The WTRU radio resource control (RRC) has a connected mode and an idle mode. The connected mode includes an active connected mode and an inactive connected mode. In the connected mode, the WTRU RRC has four states: CELL_DCH, CELL_FACH, CELL_PCH, and URA_PCH. The CELL_DCH and the CELL_FACH states take place only in the active connected mode, and the CELL_PCH and the URA_PCH states take place only in the inactive connected mode. The DRX mode takes place in the inactive connected mode, (CELL_PCH, URA_PCH states), and in the idle mode.
The basic difference between DRX in the idle mode and the connected mode is that, in the idle mode, it is the core network (CN) that controls the DRX cycle; whereas in the inactive connected mode, it is the universal mobile telecommunication system (UMTS) terrestrial radio access network (UTRAN) that controls the DRX cycle.
During DRX mode, the WTRU must wake up on Paging Occasions (POs) as directed by the RRC, based on system information settings. A PO indicates the beginning of a paging block. The RRC is responsible for scheduling the time, the duration and on which channel the physical layer of the WTRU must listen to.